“We are not characterizing them (GMO crops) as bad or good. We are just providing information,” said Michael Livingston, a government agricultural economist and one of the authors of the report, prepared by the USDA’s Economic Research Service.

The report, released online on Feb. 20, comes at a time when GMO crops are under intense scrutiny. Consumer groups are calling for tighter regulation of crop research and production and seeking mandatory labeling of foods made with GMOs; environmentalists are reporting increasing concerns about weed resistance and insect resistance to the crops and the chemicals used on them; and some scientific studies are reporting that the chemicals used on the crops are linked to disease and illness.

As well, the report comes as the USDA and the Environmental Protection Agency are in the final stages of approving the commercialization of a new GMO crop and chemical product package developed by Dow AgroSciences, a unit of Dow Chemical.

Genetically modified crops have become wildly popular with U.S. farmers since Monsanto Co introduced herbicide-tolerant “Roundup Ready” soybeans in the mid-1990s. Since then, Monsanto and other seed and chemical companies have introduced a variety of corn, soybeans, cotton, canola and others crops that tolerate being sprayed with herbicide or resist insects.

GMO crops were planted on about 169 million acres in the U.S. in 2013, about half the total land used for crops, the report said.

The seeds are patented and cost more than conventional seeds — the price of GMO soybean and corn seeds grew by about 50 percent between 2001 and 2010, according to the report. But the companies that sell them say they make weed and insect management easier for farmers and can help increase production.

But in its report, the ERS researchers said over the first 15 years of commercial use, GMO seeds have not been shown to definitively increase yield potentials, and “in fact, the yields of herbicide-tolerant or insect-resistant seeds may be occasionally lower than the yields of conventional varieties,” the ERS report states.

Several researchers have found “no significant differences” between the net returns to farmers who use GMO herbicide tolerant seeds and those who use non-GMO seeds, the report states.

GMO crops that prevent yield losses to pests is more helpful to farmers financially, allowing crops more yield potential and higher monetary returns, the report states. As well, insecticide use on corn farms was down to 0.02 pound per acre in 2010, down from 0.21 pound per acre in 1995, the report states.

But while insecticide use has gone down, herbicide use on GMO corn is rising, the report states. Herbicide use on GMO corn increased from around 1.5 pounds per planted acre in 2001 to more than 2.0 pounds per planted acre in 2010. Herbicide use on non-GMO corn has remained relatively level during that same time frame, the ERS said.

And the over reliance on glyphosate has translated to an increase in weed resistance, which makes crop production much harder. Glyphosate is the chief ingredient in Roundup herbicide sold by Monsanto, and its use has translated to the glyphosate resistance seen in 14 weed species and biotypes in the United States, according to ERS.

Researchers have thousands of tests underway in U.S. fields for new crops, ERS reported. As of September 2013, about 7,800 releases have been approved for genetically engineered corn, more than 2,200 for GE soybeans, more than 1,100 for GE cotton, and about 900 for GE potatoes.

Of those releases, 6772 were for GE varieties with herbicide tolerance, 4,809 for insect resistance, and 4,896 for product quality such as flavor or nutrition, and 5,190 for drought resistance.

Monsanto has the most authorized field releases with 6,782, followed by DuPont Pioneer, with 1,405.